US20080200973A1 - Method and system using MRI compatibility defibrillation pads - Google Patents

Abstract

In accordance with embodiments of the present technique an electrode pad for medical use is provides. The electrode pad comprises a support layer a plurality of electrodes mounted on the support layer and electrically insulated from one another, and a plurality of leads electrically coupled to the electrodes for selectively placing the electrodes at a desired electrical potential.

Description

BACKGROUND
• The present invention relates generally to defibrillation systems. Particularly, the invention relates to defibrillation pads operable in conjunction with other medical systems during various medical procedures.
• Defibrillation devices, otherwise known as defibrillators, are used to correct a medical condition known as fibrillation, which is a very rapid, disorganized twitching or trembling of the heart muscle in place of a normal rhythmic beat. To correct such a condition, a defibrillator directs a pulse of electrical direct-current (DC) into the heart to return it to its regular rhythm. To deliver such a pulse of electrical current to the heart of a patient, two defibrillation pads are attached, typically on the chest area of the patient. An electrical voltage applied between the defibrillation pads induces current through the heart of the patient, restoring the normal rhythm of the heart. Defibrillation pads are typically spread out in two dimensions, with typical lengths of several inches in each direction to provide a large contact area with the skin.
• Various medical procedures may require coupling a patient to a defibrillator, via its defibrillation pads, as a precautionary measure. This may be done in order to expedite defibrillation therapy to the patient in the event the patient does experience fibrillation during the medical procedure. However, there are instances where the defibrillator pads can interfere with the medical procedure, such that it may not be operationally practical to couple the patient to the defibrillator. For example, during magnetic resonance imaging (MRI), a patient is placed within a partial enclosure whereby the patient is surrounded by static magnetic fields, dynamically-pulsed gradient magnetic fields, and radio frequency (RF) fields. These fields are used to interact with the atomic nuclei, exciting the population of magnetic moments and detecting microscopic magnetic fields induced by precessing nuclei. Electromagnetic interactions of the gradient and RF magnetic fields with various components of the defibrillation pads, e.g., wire leads and electrodes, may induce eddy currents that could interfere with imaging signals producing patient image data. To the extent such interference effects are present during the imaging procedure, they may create image artifacts and degrade image quality. Without a means to preserve image quality in the presence of defibrillation pads, it could become unfeasible to place such pads in the proximity of the MR imaging coils and expedite delivery of therapy in the event of urgent medical need.
• There is a need in the art for improved defibrillation pads couplable to a patient during medical procedures. Particularly, there is a need for defibrillation pads couplable to a patient while the patient is situated within an MRI system such that the defibrillation pads minimally interfere with electromagnetic fields contained within the enclosure of the MRI system. There is also a need for similar pads that can be used during clinical interventional procedures such as cardiovascular ablation procedures.
BRIEF DESCRIPTION
• The present technique provides a defibrillation system based upon defibrillation pads couplable to a patient while the patient undergoes a medical procedure. In accordance with embodiments of the present technique, the defibrillation pads are operable within an imaging device such as an MRI device. Accordingly, the provided defibrillation pads and components thereof are configured to minimally interfere with electromagnetic signals produced by the MRI device. In this manner, image artifacts are minimized to the extent the images can provide desirable information relating to the patient to a clinician. Further, the present technique enables use of the defibrillation pads within the patient volume of the MRI device, thus eliminating time delays otherwise incurred in situations requiring exiting the patient from the MRI system before defibrillation pads can be applied to the patient.
• The present technique further enables utilizing pads with similar geometry as defibrillation pads in other medical procedures, such as cardiovascular ablation procedures, whereby a conducting pad disposed on a patient provides an electrical ground connection for an ablation device.
DRAWINGS
• These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
• FIG. 1 illustrates defibrillation pads disposed on a patient in accordance with an embodiment of the present technique;
• FIG. 2 illustrates a segmented defibrillation pad in accordance with an embodiment of the present technique;
• FIG. 3 is a side view of a packaged defibrillation pad in accordance with an embodiment of the present technique;
• FIG. 4 is a side view of a defibrillation pad in accordance with an embodiment of the present technique; and
• FIG. 5 illustrates defibrillation pads used in conjunction with a patient imaging device in accordance with an embodiment of the present technique.
DETAILED DESCRIPTION
• Turning now to the drawings and referring toFIG. 1, twodefibrillation pads12 disposed on a chest area of apatient14 are shown, in accordance with an embodiment of the present technique. Each ofdefibrillation pads12 are generally couplabe to adefibrillation control system16 viawire lead18.Defibrillation control system16 may be a generic defibrillation system having connections compatible with multiple types and/or brands of defibrillation pads,such defibrillation pads12. While the present embodiment illustrates two defibrillation pads coupled tocontrol system16, other embodiments may include more than two defibrillation pads, such asdefibrillation pads12, coupled tocontrol system16.Defibrillation pads12 may be coupled todefibrillation control system16 using plugs, clips, caps and so forth. Such coupling devices enable delivery of voltages and currents, such as those desired during defibrillation treatments, to and frompads12. While in the illustrated embodiment,defibrillation pads12 are disposed on the chest area ofpatient14, in other embodiments the defibrillation pads may be configured to be disposed on, for example, a back side the patient or other suitable anatomical parts ofpatient14. Accordingly, during, for example, a cardiac ablation procedure, one or more of the pads (although in such application not used for defibrillation) may be disposed on the patient so as to provide an electrical ground connection. In such a procedure, it may be desirable to place one of thedefibrillation pads12 on the back area of the patient.
• As further discussed below,defibrillation pads12 may be coupled to the patient via an adhesive and/or a gel that securely attachesdefibrillation pads12 topatient14. Such an adhesive and/or gel may also be configured to conduct electric current betweenpads12 andpatient14, thereby ensuring that a desirable level of current is delivered to the patient when voltage is applied to the defibrillation pads viadefibrillation control system16.
• As depicted byFIG. 1, each of the defibrillation pads may be partitioned intosegments20, such that each segment may be separately couplabe to wire leads18. Accordingly, eachdefibrillation pad12 may be formed fromindividual segments20 containing electrodes (FIG. 2), such that each electrode may be independently coupled to a voltage supply provided bydefibrillation control16. Hence, it should be borne in mind that wire leads18, shown inFIG. 1, may actually be formed of strands of wire, such that each strand of wire leads to an electrode disposed withinpad segments20. As discussed below, the segmentation of the pads allows each pad to provide coverage and current comparable to conventional defibrillation pads, while limiting eddy currents within and around the pads due to the reduced size of each of the segments as compared to the overall size of the pad.
• FIG. 2 illustrates schematically an implementation of a defibrillation pad, such as defibrillation pad12 (FIG. 1), in accordance with an exemplary embodiment of the present technique. As depicted byFIG. 2,defibrillation pad12 is segmented intomultiple segments20, such that each segment includes anelectrode22.Electrodes22 may be formed of a conductive material, such as metallic foil, suitable for delivering electrical current to and frompad12. Each of theelectrodes22 is separately coupled, viaconnection point28, to awire lead24 independently coupling each of the electrodes to a voltage supply through aswitch25 which in some embodiments may be part ofdefibrillation controller16. In the illustrated embodiment,switch25 is separate fromdefibrillation controller16 such thatleads24 are routed through the switch from which a single wire lead, such as one of wire leads18, is provided todefibrillation controller16.
• Switch25 is adapted to connect or disconnect each ofleads24 fromdefibrillation controller16 so that, for example, whenpads12 are not in use, switch25 (in an open state) electrically disconnects each ofleads24 from a power source, as well as from theother leads24. Hence,switch25 and the manner in which the defibrillation pads are segmented, as further described below, enables obtaining electrical configurations minimizing the extent to which eddy currents may interfere with surrounding electromagnetic fields aboutdefibrillation pads12 while the defibrillation system is idle. When the defibrillation system is in use,switch25 is switched to a closed state, whereby each ofleads24 is placed at a desirable electrical potential anddefibrillation pads12 become electrically connected.
• It should be borne in mind that the segmentation ofpad12 shown above is exemplary and that alternative segmentation patterns ofpad12 are possible, and within the scope of the invention, so as to accommodate various operational needs. For example, the number and shape of the segments may be varied to achieve the desired effects. That is, leads18,24 andelectrodes22 and the manner in which those elements are disposed throughoutpads12 and theirsegments20 may determine the extent to which eddy currents produced by these elements influence a particular medical procedure in which the defibrillation pads are applied to the patient. Accordingly, certain medical procedures may require that defibrillation pads, such asdefibrillation pads12, be custom segmented in a manner which minimizes their interaction with the medical procedure, typically their interfering electromagnetic fields resulting from eddy current generation.
• When thedefibrillation pad12 is in operation, each of theelectrodes24 is configured to sustain an electrical current such that the overall current delivered to or from theelectrodes22 conforms to a desirable electrical current used in defibrillation treatments. Further, partitioningpad12 into individual segments, such assegments20, reduces the overall magnitude of eddy currents produced byelectrodes22 and wire leads24, and by the conductive components of the pads themselves. In other words, by segmenting the overall conductive area of each pad, connecting eachelectrode22 separately to a voltage supply, and placing a plurality of such electrodes throughoutpad12, eddy currents due to changing magnetic fields are reduced. It should be borne in mind that the electrical configuration shown inFIG. 2, whereby eachelectrode22 is separately coupled to a voltage supply vialeads24 is an exemplary configuration. As mentioned above, other electrical configurations of disposing andwiring electrodes22 and leads24 throughoutpads12 can be envisioned, resulting in an overall reduction of eddy currents acrosspads12, as compared to conventional unsegmented pads. For example, it may be possible to connect allelectrodes24 disposed in a single row or a single column to a common lead, such that each row or column ofpad12 is separately connected to the voltage supply. This electrical configuration may, too, diminish eddy currents across thepad12 which could optimally accommodate certain operational and/or clinical conditions arising in a specific medical procedure.
• FIG. 3 is a side view of a packaged defibrillation pad, such asdefibrillation pad12, in accordance with an embodiment of the present technique. Accordingly,FIG. 3 depicts a packaged defibrillation pad, such asdefibrillation12, such that the pad is enveloped by aremovable cover30.Removable package30 is configured to securely protectdefibrillation pad12 while the pad is stored and is not in use. Accordingly,package30 may protect and preservepad12 from humidity or other corrosive elements or materials that otherwise would compromise electrical and/or mechanical components of the pad throughout its storage period.Package30 may be formed of plastic, nylon, paper, styrofoam, combinations of these, or any other material that can be readily opened providing easy and fast access topad12. The package also may keep the pad sterile during transport and storage.
• As further shown byFIG. 3,defibrillation pad segments20,electrodes22 and wire leads24 are supported by asubstrate32 which may be formed of paper or a plastic material.Substrate32 provides structural support forelectrodes22 and wire leads24, as well as proper electrical insulation betweenelectrodes22 and leads24.Substrate32 may be coupled topad segments20,electrodes22 and/or to wire leads24 via anadhesive layer34 disposed on the inner surface ofsubstrate32, i.e., the surface ofsubstrate32 facingelectrodes22 and wire leads24.
• Packageddefibrillation pad12 further includes anadhesive layer36 disposed on a side of the pad facing away from theelectrodes22 and wire leads24. Accordingly, adhesive36 is configured to securely affixpad12, specificallyelectrodes22, to the patient so as to ensure thatpad12 is retained on the patient for a prolonged period of time, as would be needed throughout a medical procedure in which defibrillation pads are employed. Further,adhesive layer36 ensures that a suitable electrical contact exists between the patient andelectrodes22. Accordingly,adhesive layer36 may be formed of materials having mechanical, electrical and/or thermal properties suited for interfacing between the defibrillation pads and the patient.
• Defibrillation pad12 further includes agel layer38 disposed overadhesive layer36.Gel layer38 is configured to enhance electrical coupling between theelectrodes22 and a patient to whichpad12 is applied. In other words,gel38 may improve the electrical conductivity between the patient and the pad so as to better facilitate current flow to and from the pad during defibrillation. Such gels may be similar to those used conventionally on electrocardiograph and similar electrodes.
• FIG. 4 is a side view of a defibrillation pad, such as thedefibrillation pad12 ofFIG. 1, in accordance with an embodiment of the present technique.FIG. 4 illustrates anunpackaged defibrillation pad12, ready for use as it would be applied to a patient. Accordingly,gel layer38 provides an interface betweenpad12 and the patient. As may be appreciated by those of ordinary skilled in the art,gel layer38 may also be disposed on the patient beforepad12 is applied thereto. When applyingpad12 to the patient, pressingsubstrate32 ofpad12 against the body of the patient may thin thegel layer38 such thatadhesive layer36 may adherepad segments20 and, thus,electrodes22 to the body of the patient.
• As further illustrated byFIG. 4, wire leads24 may extend throughout thepad12 connecting each electrode, or alternatively a plurality of electrodes, to wirelead18. Accordingly, wire leads24 may be disposed alongpad12, providing sufficient slack to theextent pad segments20 andsubstrate32 can flex and conform to various curvatures and/or shapes of anatomical regions to whichpad12 is applied.
• FIG. 5 is a diagrammatical representation of an imaging device such as an MRI system for use in medical diagnostic imaging and implementing use of a defibrillation system according to the present technique. TheMRI system50 suitable for MR diagnostic imaging and/or tracking is illustrated diagrammatically as including ascanner52,scanner control circuitry54, andoperator interface station56. WhileMRI system50 may include any suitable MRI scanner or detector, in the illustrated embodiment the system includes a full body scanner comprising a patient bore58 into which a table60 may be positioned to place apatient62 in a desired position for scanning.
• As illustrated byFIG. 5,patient62 is coupled to a defibrillation control system, such as thedefibrillation system16 shown inFIG. 1, viadefibrillation pads12 coupled to wire leads18 connected the defibrillation control system. In the illustrated embodiment, the defibrillation pads are applied to the chest area ofpatient62 undergoing imaging and/or tracking. Couplingpatient62 to a defibrillator while the patient undergoes a medical procedure, such as the one depicted byFIG. 5, may be desirable in an event the patient experiences fibrillation requiring defibrillation therapy. Under such conditions, defibrillation can be applied expeditiously while the patient remains in patient bore58 such that no time is wasted on exiting the patient62 frombore58 before defibrillation can be performed.
• As illustrated inFIG. 5, adevice64 to be tracked may be inserted intopatient62 by anoperator65.Device64 may be any suitable device for use in a medical or surgical procedure.Device64 may be a guide wire, a catheter, an endoscope, a laparoscope, a biopsy needle, an ablation device or other similar devices. For example, in an ablation procedure one pad, essentially identical to thedefibrillation pads12 discussed above, may be employed toelectrically ground patient62 so as to close an electrical loop with the ablation device applied to the patient. In such an embodiment, the grounding pad may be placed, for example, on the back area of the patient.
• Further, non-invasive devices, such as external coils used in tracking, are also within the scope of the present embodiments. In such embodiments,device64 may include an RF tracking coil66 for receiving emissions from gyromagnetic material. Tracking coil66 may be mounted, for example, in the operative end ofdevice64. Tracking coil66 also may serve as a transmitting coil for generating radio frequency pulses for exciting the gyromagnetic material. Thus, tracking coil66 may be coupled with driving and receiving circuitry in passive and active modes for receiving emissions from the gyromagnetic material and for applying RF excitation pulses, respectively. Hence, in a procedure utilizing RF tracking, wiring ofdefibrillation pads12 may interact with the RF signals produced by the tracking the tracking device and RF coils so as to minimize generation of eddy currents.
• Referring again toMRI system50,scanner52 includes a series of associated coils for producing controlled magnetic fields, for generating RF excitation pulses, and for detecting emissions from gyromagnetic material within the patient in response to such pulses. In the diagrammatical view ofFIG. 5, aprimary magnet coil68 is provided for generating a primary magnetic field generally aligned with patient bore58. A series of gradient coils70,72 and74 are grouped in a coil assembly for generating controlled magnetic gradient fields during examination sequences. Aradio frequency coil76 is provided for generating RF pulses for exciting the gyromagnetic material. In the embodiment illustrated inFIG. 5,RF coil76 also serves as a receiving coil. Thus,RF coil76 may be coupled with driving and receiving circuitry in passive and active modes for receiving emissions from the gyromagnetic material and for applying radiofrequency excitation pulses, respectively. Alternatively, various configurations of receiving coils may be provided separate fromRF coil76. Such coils may include structures specifically adapted for target anatomies, such as head coil assemblies, and so forth. Moreover, receiving coils may be provided in any suitable physical configuration, including phased array coils, and so forth. The magnetic and RF fields produced by the gradient coils70,72 and74 and theRF coil76, respectively, interact with thedefibrillation pads12 to the extent eddy current produced by such interactions have no significant affect on gyromagnetic pulses obtained from the tissue ofpatient62.
• The coils ofscanner52 are controlled by external circuitry to generate desired fields and pulses, and to read signals from the gyromagnetic material in a controlled manner. As will be appreciated by those skilled in the art, when the material, typically bound in tissues of the patient, is subjected to the primary field, individual magnetic moments of the magnetic resonance-active nuclei in the tissue partially align with the field. While a net magnetic moment is produced in the direction of the polarizing field, the randomly oriented components of the moment in a perpendicular plane generally cancel one another. During an examination sequence, an RF frequency pulse is generated at or near the Larmor frequency of the material of interest, resulting in rotation of the net aligned moment to produce a net transverse magnetic moment. This transverse magnetic moment precesses around the main magnetic field direction, emitting RF (magnetic resonance) signals. For reconstruction of the desired images, these RF signals are detected byscanner50 and processed. For location ofdevice64, these RF signals are detected by RF tracking coil66 mounted indevice64 and processed. As mentioned above, the minimal interaction of the defibrillation pads12 (FIG. 1), with the magnetic field and RF pulses produced byscanner52 results in images having reduced artifacts that otherwise would be noticeable with conventional defibrillation pads used within an MRI system, such as that shown inFIG. 5.
• Further, the coils ofscanner52 are controlled byscanner control circuitry54 to generate the desired magnetic field and RF pulses. In the diagrammatical view ofFIG. 5,control circuitry54 thus includes acontrol circuit80 for commanding the pulse sequences employed during the examinations, and for processing received signals. For example,control circuit80 applies analytical routines to the signals collected in response to the RF excitation pulses to reconstruct the desired images and to determine device location.Control circuit80 may include any suitable programmable logic device, such as a CPU or digital signal processor of a general purpose or application-specific determiner. Control circuitry further includesablation controller81 coupled toablation device64.Ablation controller81 is configured to supply power toablation device64 so as to control voltage and current magnitudes used in ablation procedures.Control circuitry54 further includesmemory circuitry82, such as volatile and non-volatile memory devices for storing physical and logical axis configuration parameters, examination pulse sequence descriptions, acquired image data, acquired tracking data, programming routines, and so forth, used during the examination sequences implemented byscanner52. In the illustratedembodiment defibrillation controller16 is shown as separate fromcontrol circuitry56, however, in other embodiments the defibrillation controller may be included incontrol circuitry54.
• Interface between thecontrol circuit80 and the coils ofscanner52 anddevice64 is managed by amplification andcontrol circuitry84 and by transmission and receiveinterface circuitry86.Circuitry84 includes amplifiers for each gradient field coil to supply drive current to the field coils in response to control signals fromcontrol circuit80.Interface circuitry86 includes additional amplification circuitry for drivingRF coil76. Moreover, whereRF coil76 serves both to emit the radiofrequency excitation pulses and to receive MR signals,circuitry86 will typically include a switching device for toggling theRF coil76 between active or transmitting mode, and passive or receiving mode.Interface circuitry86 further includes pre-amplification circuitry to amplify the signals received by RF tracking coil66 mounted indevice64. Furthermore, where RF tracking coil66 serves as both a transmitting coil and a receiving coil,circuitry86 will typically include a switching device for toggling RF tracking coil66 between active or transmitting mode, and passive or receiving mode. Finally,circuitry54 includesinterface components88 for exchanging configuration and image and tracking data withoperator interface station56. Hence, in situations, such as those described above, where RF signals are amplified or otherwise modified, wirings of wire leads24 withelectrodes22 may be modified accordingly to obtain an electrical configuration of those elements which interact minimally with the RF and magnetic fields.
• Operator interface station56 may include a wide range of devices for facilitating interface between an operator or radiologist andscanner52 viascanner control circuitry54. In the illustrated embodiment, for example, anoperator controller90 is provided in the form of a determiner work station employing a general purpose or application-specific determiner.Operator controller90 may be coupled to interface88 ofcontroller circuitry54, as well as todefibrillator controller16, so that an operator may monitor and control parameters pertinent to the mechanical procedure. The station also typically includes memory circuitry for storing examination pulse sequence descriptions, examination protocols, user and patient data, image data, both raw and processed, and so forth. The station may further include various interface and peripheral drivers for receiving and exchanging data with local and remote devices. In the illustrated embodiment, such devices include aconventional determiner keyboard92 and an alternative input device such as amouse94. Aprinter96 is provided for generating hard copy output of documents and images reconstructed from the acquired data. A determiner monitor98 is provided for facilitating operator interface. In addition,system50 may include various local and remote image access and examination control devices, represented generally byreference numeral100 inFIG. 5. Such devices may include picture archiving and communication systems, teleradiology systems, and the like.
• While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

Claims (21)

1. An electrode pad for medical use, comprising:

a support layer;

a plurality of electrodes mounted on the support layer and electrically insulated from one another; and

a plurality of leads electrically coupled to the electrodes for selectively placing the electrodes at a desired electrical potential.

2. The pad ofclaim 1, comprising an adhesive region on or adjacent to the electrodes for adhesively securing the pad to the skin of a patient.

3. The pad ofclaim 1, comprising a conductive gel disposed over the electrodes.

4. The pad ofclaim 1, wherein the electrodes are made of a metallic foil.

5. An electrode pad kit for medical use, comprising:

a support layer;

a plurality of electrodes mounted on the support layer and electrically insulated from one another;

a plurality of leads electrically coupled to the electrodes;

means for coupling the leads to an electrical system to selectively place the electrodes at a desired electrical potential;

an adhesive region on or adjacent to the electrodes for adhesively securing the pad to the skin of a patient; and

a removable layer disposed over the electrodes and the adhesive region.

6. The kit ofclaim 5, comprising a conductive gel disposed over the electrodes.

7. The kit ofclaim 5, wherein the electrodes are made of a metallic foil.

8. A defibrillator system comprising:

a plurality of defibrillator pads, each pad including a support layer, a plurality of electrodes mounted on the support layer and electrically insulated from one another, and a plurality of leads electrically coupled to the electrodes, the pads being configured to be removably secured to the skin of a patient; and

a defibrillator controller coupled to the electrodes and configured to selectively place the electrodes of each pad at a desired potential for causing a current to flow through the patient.

9. The system ofclaim 8, wherein each pad includes an adhesive region on or adjacent to the electrodes for adhesively securing the pad to the skin of a patient.

10. The system ofclaim 8, wherein each pad includes a conductive gel disposed over the electrodes.

11. The system ofclaim 8, wherein the electrodes are made of a metallic foil.

12. The system ofclaim 8, comprising a switch coupled to at least one of the defibrillation pads and to the defibrillation controller, wherein the switch is configured to electrically connect and disconnect each one of the plurality of leads to and from a power source.

13. A method for imaging a patient anatomy comprising:

securing an electrode pad to a patient, the pad comprising a support layer, a plurality of electrodes mounted on the support layer and spaced from one another, and a plurality of leads electrically coupled to the electrodes for selectively placing the electrodes at a desired electrical potential;

placing the patient in an MR imaging system;

controlling the MR imaging system to produce image data for reconstruction of anatomies of interest within the patient.

14. The method ofclaim 13, comprising securing a plurality of similar electrode pads to the patient, and electrically coupling the electrode pads to a defibrillation controller.

15. The method ofclaim 14, wherein the pad includes an adhesive region on or adjacent to the electrodes for adhesively securing the pad to the skin of a patient.

16. The method ofclaim 14, wherein the pad includes a conductive gel disposed over the electrodes.

17. The method ofclaim 14, wherein the electrodes are made of a metallic foil.

18. A cardiac ablation system comprising:

a catheter insertable into a patient and having a conductive tip for applying a first desired potential to tissues of interest for ablation;

a conductive pad including a support layer, a plurality of electrodes mounted on the support layer and spaced from one another, and a plurality of leads electrically coupled to the electrodes for applying a second desired potential to the electrodes, the pad being configured to be removably secured to the skin of a patient; and

an ablation controller coupled to the catheter and to the electrodes and configured to selectively place the catheter tip and the electrodes of the pad at the first and second desired potentials for ablation of the tissues of interest.

19. The system ofclaim 18, comprising a device to be tracked coupled to the catheter.

20. The system ofclaim 19, wherein the device to be tracked is tracked via an imaging device.

21. The system ofclaim 20, wherein the imaging device is a magnetic resonance scanner.

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